Variable displacement vane pump

ABSTRACT

A variable displacement vane pump includes: a restrictor configured to impart resistance to flow of working fluid discharged from the pump chambers; a control valve configured to introduce the working fluid which is discharged from the pump chambers to the first fluid pressure chamber as a differential pressure between upstream and downstream of the restrictor is increased, the control valve being configured to discharge the working fluid in the first fluid pressure chamber as the differential pressure between upstream and downstream of the restrictor is reduced; a suction passage configured to guide the working fluid to be sucked into the pump chambers, the suction passage being configured to always communicate with the second fluid pressure chamber; and a guiding passage configured to allow communication between the control valve and the second fluid pressure chamber, the guiding passage being configured to guide the working fluid, which is discharged from the first fluid pressure chamber to the control valve, to the second fluid pressure chamber.

TECHNICAL FIELD

The present invention relates to a variable displacement vane pump usedas a fluid pressure source.

BACKGROUND ART

JP2013-194692A describes a variable displacement vane pump that iscapable of changing an amount of working fluid discharged by changing anamount of eccentricity of a cam ring with respect to a rotor.

In order to move the cam ring, this variable displacement vane pumpincludes a first fluid pressure chamber and a second fluid pressurechamber that are formed on the outer circumferential side of the camring; a metering orifice that is provided in a discharge passage; acontrol valve that introduces control pressure to the first fluidpressure chamber in accordance with movement of a spool that slides inaccordance with a differential pressure between upstream and downstreamof the metering orifice; and a cam spring that always biases the camring towards the first fluid pressure chamber side from the second fluidpressure chamber. The cam ring is provided so as to be movable between amaximum-eccentric position in which the amount of eccentricity ismaximized when the cam ring is moved towards the first fluid pressurechamber side and a minimum-eccentric position in which the amount ofeccentricity is minimized.

SUMMARY OF INVENTION

In the above-described conventional technique, while the controlpressure is introduced to the first fluid pressure chamber from thecontrol valve, suction pressure is always introduced to the second fluidpressure chamber. Therefore, when the cam ring is moved in the directionin which the amount of eccentricity is reduced, the cam ring is moved bythe control pressure introduced to the first fluid pressure chamber.However, when the cam ring is moved in the direction in which the amountof eccentricity is increased, the cam ring is moved by biasing forceexerted by the cam spring. Thus, there is a risk in that, when the camring is moved in the direction in which the amount of eccentricity isincreased, the movement of the cam ring may be delayed, causing afollow-up delay.

The present invention has been conceived in light of such technicalproblems, and an object thereof is to provide a variable displacementvane pump capable of preventing the follow-up delay of a cam ring.

According to one aspect of the present invention, a variabledisplacement vane pump includes: a rotor that is linked to a drivingshaft; a plurality of vanes provided so as to be movable in areciprocating manner in the radial direction with respect to the rotor;a cam ring in which tip-end portions of the vanes are in sliding contactwith a cam face on an inner circumference of the cam ring with rotationof the rotor arranged in the cam ring, the cam ring being capable ofbeing made eccentric with respect to the rotor; pump chambers that aredefined between the rotor and the cam ring by being partitioned by theplurality of vanes; a first fluid pressure chamber and a second fluidpressure chamber that are defined in an accommodating space on an outercircumferential side of the cam ring; a biasing member configured toalways bias the cam ring in a direction in which an amount ofeccentricity is increased; a restrictor configured to impart resistanceto flow of working fluid discharged from the pump chambers; a controlvalve configured to reduce the amount of eccentricity of the cam ring byintroducing the working fluid that has been discharged from the pumpchambers to the first fluid pressure chamber as a differential pressurebetween upstream and downstream of the restrictor is increased, thecontrol valve being configured to increase the amount of eccentricity ofthe cam ring by discharging the working fluid in the first fluidpressure chamber as the differential pressure between upstream anddownstream of the restrictor is reduced; a suction passage configured toguide the working fluid to be sucked into the pump chambers, the suctionpassage being configured to always communicate with the second fluidpressure chamber; and a guiding passage configured to allowcommunication between the control valve and the second fluid pressurechamber, the guiding passage being configured to guide the workingfluid, which is discharged from the first fluid pressure chamber to thecontrol valve, to the second fluid pressure chamber.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a sectional view showing a cross section perpendicular to adriving shaft in a variable displacement vane pump according to a firstembodiment of the present invention.

FIG. 2 is a sectional view showing a cross section parallel to thedriving shaft in the variable displacement vane pump according to thefirst embodiment of the present invention.

FIG. 3 is a hydraulic circuit diagram of the variable displacement vanepump according to the first embodiment of the present invention.

FIG. 4 is a hydraulic circuit diagram of the variable displacement vanepump according to the first embodiment of the present invention andshows a state in which an amount of eccentricity of a cam ring withrespect to a rotor is at a maximum level.

FIG. 5 is a hydraulic circuit diagram of the variable displacement vanepump according to the first embodiment of the present invention andshows a state in which the amount of eccentricity of the cam ring withrespect to the rotor is at an intermediate level.

FIG. 6 is a hydraulic circuit diagram of the variable displacement vanepump according to the first embodiment of the present invention andshows a state in which the amount of eccentricity of the cam ring withrespect to the rotor is at a minimum level.

FIG. 7 is a sectional view showing a cross section perpendicular to adriving shaft in a variable displacement vane pump according to a secondembodiment of the present invention.

FIG. 8 is a sectional view showing a cross section parallel to thedriving shaft in the variable displacement vane pump according to thesecond embodiment of the present invention.

DESCRIPTION OF EMBODIMENTS

The following describes embodiments of the present invention withreference to the drawings.

First Embodiment

A variable displacement vane pump 100 according to a first embodiment ofthe present invention will be described with reference to FIGS. 1 to 3.

The variable displacement vane pump 100 (hereinafter, simply referred toas “the vane pump 100”) is used as a hydraulic pressure source for ahydraulic apparatus mounted on a vehicle, such as, for example, a powersteering apparatus, a continuously variable transmission, and the like.

As shown in FIG. 1, in the vane pump 100, motive force from a drivingsource (not shown) is transmitted to a driving shaft 1, and a rotor 2that is linked to the driving shaft 1 is rotated. In FIGS. 1 and 3, therotor 2 is rotated in the counterclockwise direction as indicated by anarrow.

The vane pump 100 includes a plurality of vanes 3 that are provided soas to be movable in a reciprocating manner in the radial direction withrespect to the rotor 2 and a cam ring 4 in which tip-end portions of thevanes 3 are in sliding contact with a cam face 4 a, forming an innercircumference of the cam ring 4, by rotation of the rotor 2 arranged inthe cam ring 4. The cam ring 4 is can be made eccentric with respect tothe center of the rotor 2.

As shown in FIG. 2, the driving shaft 1 is rotatably supported by a pumpbody 6 via a bush 5. A pump accommodating recessed portion 6 a servingas a recessed portion for accommodating the cam ring 4 is formed in thepump body 6. In an end portion of the pump body 6, a seal 7 is providedfor preventing leakage of lubricating oil between an outer circumferenceof the driving shaft 1 and an inner circumference of the bush 5.

A side plate 8 that comes into contact with first side portions of therotor 2 and the cam ring 4 is arranged on a bottom surface 6 b of thepump accommodating recessed portion 6 a. An opening portion of the pumpaccommodating recessed portion 6 a is sealed with a pump cover 9 thatcomes into contact with second side portions of the rotor 2 and the camring 4. The pump cover 9 is fastened to the pump body 6 by bolts 10 (seeFIG. 1).

As described above, the pump cover 9 and the side plate 8 are arrangedso as to sandwich the rotor 2 and the cam ring 4 at both side surfacesthereof. With such a configuration, pump chambers 11 are defined betweenthe rotor 2 and the cam ring 4 by being partitioned by the respectivevanes 3.

As shown in FIGS. 1 and 3, the cam ring 4 is an annular member and has asuction region in which volumes of the pump chambers 11 partitioned byand between the respective vanes 3 are expanded by the rotation of therotor 2 and a discharge region in which the volumes of the pump chambers11 partitioned by and between the respective vanes 3 are contracted bythe rotation of the rotor 2. The pump chambers 11 suck working oilserving as working fluid in the suction region and discharge the workingoil in the discharge region. In FIG. 1, an upper part of the cam ring 4corresponds to the suction region and a lower part corresponds to thedischarge region.

An annular adapter ring 12 is fitted to an inner circumferential surfaceof the pump accommodating recessed portion 6 a so as to surround the camring 4. The adapter ring 12 is sandwiched by the pump cover 9 and theside plate 8 at both side surfaces thereof in the same way as the rotor2 and the cam ring 4.

A support plate 13 that extends in parallel with the driving shaft 1 issupported on an inner circumferential surface of the adapter ring 12.The cam ring 4 is supported by the support plate 13, and the cam ring 4swings around inside the adapter ring 12 with the support plate 13 as asupporting point.

A groove 12 a extending in parallel with the driving shaft 1 is formedat an axisymmetric position to the support plate 13 in the innercircumferential surface of the adapter ring 12. A seal member 14, whichis in sliding contact with the outer circumferential surface of the camring 4 when the cam ring 4 swings around, is fitted in the groove 12 ain a state in which an elastic member 15 is compressed.

As described above, in a space between the outer circumferential surfaceof the cam ring 4 and the inner circumferential surface of the adapterring 12, which is an accommodating space on the outer circumference ofthe cam ring 4, a first hydraulic chamber 16 serving as a first fluidpressure chamber and a second hydraulic chamber 17 serving as a secondfluid pressure chamber are defined by the support plate 13 and the sealmember 14.

As shown in FIG. 1, a cam spring 18 serving as a biasing member isprovided on the second hydraulic chamber 17 side of the outercircumferential surface of the cam ring 4. The cam spring 18 is fittedto a spring plug 19 that is screwed into the pump body 6 from the sideand always biases the cam ring 4 towards the first hydraulic chamber 16side via a through hole 12 b formed in the adapter ring 12. In otherwords, the cam ring 4 is always biased by the cam spring 18 in thedirection in which an amount of eccentricity is increased.

The cam ring 4 swings around with the support plate 13 as the supportingpoint in such a manner that a differential pressure of the working oilbetween the first hydraulic chamber 16 and the second hydraulic chamber17, biasing force exerted by the cam spring 18, and the internalpressure of the cam ring 4 are balanced. As the cam ring 4 swings aroundwith the support plate 13 as the supporting point, the amount ofeccentricity of the cam ring 4 with respect to the rotor 2 is changed.As the amount of eccentricity of the cam ring 4 is changed, a pumpdisplacement volume per rotation of the rotor 2 is changed.

When the pressure in the first hydraulic chamber 16 is increased, theamount of eccentricity of the cam ring 4 with respect to the rotor 2 isreduced. In this case, the pump displacement volume per rotation of therotor 2 is reduced. In contrast, when the pressure in the firsthydraulic chamber 16 is reduced, the amount of eccentricity of the camring 4 with respect to the rotor 2 is increased. In this case, the pumpdisplacement volume per rotation of the rotor 2 is increased. Asdescribed above, in the vane pump 100, the pump displacement volume ischanged in accordance with the amount of eccentricity of the cam ring 4with respect to the rotor 2.

The pump cover 9 is provided with a suction port 20 having an arc-shapedopening so as to correspond to the suction region of the pump chambers11. In addition, the side plate 8 is provided with a discharge port 21having an arc-shaped opening so as to correspond to the discharge regionof the pump chambers 11.

As shown in FIG. 2, the suction port 20 is formed so as to communicatewith a suction passage 22 formed in the pump cover 9 and guides theworking oil in the suction passage 22 to the suction region of the pumpchambers 11. The discharge port 21 is formed so as to communicate with ahigh-pressure chamber 23 formed in the pump body 6 and guides theworking oil discharged from the discharge region of the pump chambers 11to the high-pressure chamber 23.

The high-pressure chamber 23 is defined by closing a groove portion 6 c,which is formed so as to open at the bottom surface 6 b of the pumpaccommodating recessed portion 6 a, with the side plate 8. The workingoil in the high-pressure chamber 23 is guided to an external hydraulicapparatus of the vane pump 100 through a discharge passage 24 (see FIG.3) formed in the pump body 6.

The pump body 6 is provided with a low-pressure chamber 25, serving as afirst guiding passage, that is formed at a position corresponding to thesuction region of the pump chambers 11 on the bottom surface 6 b of thepump accommodating recessed portion 6 a. The low-pressure chamber 25 isdefined by closing a groove portion 6 d, which is formed so as to openat a position corresponding to the suction region of the pump chambers11, with the side plate 8. The low-pressure chamber 25 is formed in astraight line parallel to the driving shaft 1, and its back-most endportion communicates with a boundary between the bush 5 and the seal 7.The low-pressure chamber 25 is always connected to the second hydraulicchamber 17, and the working oil that has leaked out between the outercircumference of the driving shaft 1 and the inner circumference of thebush 5 is recovered and returned to the pump chambers 11 in the suctionregion.

As shown in FIGS. 1 and 2, the pump body 6 is provided with a valveaccommodating hole 26 that is formed in the direction perpendicular tothe axial direction of the driving shaft 1. In the valve accommodatinghole 26, a control valve 27 that controls the working oil pressures inthe first hydraulic chamber 16 and the second hydraulic chamber 17 isaccommodated. The valve accommodating hole 26 is sealed by a plug 28.

The control valve 27 includes a spool 29 that is slidably inserted intothe valve accommodating hole 26, a first pilot chamber 30 that faces oneend of the spool 29, a second pilot chamber 31 that faces the other endof the spool 29, and a return spring 32 that is accommodated in thesecond pilot chamber 31 and biases the spool 29 in the direction inwhich the volume of the second pilot chamber 31 is expanded.

The spool 29 includes a first land portion 29 a and a second landportion 29 b that slide along an inner circumferential surface of thevalve accommodating hole 26, an annular groove 29 c that is formedbetween the first land portion 29 a and the second land portion 29 b, afirst rod portion 29 d that is connected to the first land portion 29 aand extends within the first pilot chamber 30, and a second rod portion29 e that is connected to the second land portion 29 b and extendswithin the second pilot chamber 31.

The first rod portion 29 d comes into contact with the plug 28 when thespool 29 is moved in the direction in which the volume of the firstpilot chamber 30 is contracted. When the spool 29 is moved in thedirection in which the volume of the second pilot chamber 31 iscontracted, the second rod portion 29 e comes into contact with an endsurface of the valve accommodating hole 26 on the opposite side from theplug 28. The return spring 32 surrounds the second rod portion 29 e andis received in the second pilot chamber 31.

As shown in FIG. 3, a first passage 35 and a second passage 36, whichserves as a guiding passage, that communicate with the first hydraulicchamber 16 and the second hydraulic chamber 17, respectively; a firstpressure guiding passage 38 that guides to the first pilot chamber 30the working oil that has been discharged from the high-pressure chamber23 to the upstream side of an orifice 37 serving as a restrictor; and asecond pressure guiding passage 39 that guides to the second pilotchamber 31 the working oil that has been discharged from thehigh-pressure chamber 23 to the downstream side of the orifice 37 areconnected to the control valve 27. A drain passage 40 that is always incommunication with the suction passage 22 is connected to the secondhydraulic chamber 17.

The first passage 35 and the second passage 36 are formed so as to openat the valve accommodating hole 26 and to open at the first hydraulicchamber 16 and the second hydraulic chamber 17, respectively, bypenetrating through the adapter ring 12.

The spool 29 slides to a position at which the thrust force exerted bythe differential pressure between the first pilot chamber 30 and thesecond pilot chamber 31, which face the respective ends of the spool 29,is balanced with the biasing force exerted by the return spring 32. Thefirst passage 35 is opened/closed by the first land portion 29 a, andthe working oil in the first hydraulic chamber 16 is supplied/dischargeddepending on the position of the spool 29. The second passage 36 alwaysopens to the annular groove 29 c regardless of the position of the spool29.

When the biasing force exerted by the return spring 32 is greater thanthe thrust force exerted by the differential pressure between the firstpilot chamber 30 and the second pilot chamber 31, a state in which thereturn spring 32 is elongated is achieved. In this state, as shown inFIGS. 1 and 3, the first passage 35 and the second passage 36 open atthe annular groove 29 c. With such a configuration, the communicationbetween the first hydraulic chamber 16 and the first pilot chamber 30 isshut off.

Here, a state in which the first hydraulic chamber 16 communicates withthe drain passage 40 through the first passage 35, the annular groove 29c, the second passage 36, and the second hydraulic chamber 17 isachieved. Because the cam ring 4 is always biased by the cam spring 18in the direction in which the amount of eccentricity is increased, theamount of eccentricity of the cam ring 4 with respect to the rotor 2 ismaximized.

In contrast, when the thrust force exerted by the differential pressurebetween the first pilot chamber 30 and the second pilot chamber 31 isgreater than the biasing force exerted by the return spring 32, thespool 29 is moved against the biasing force exerted by the return spring32. In this case, the first passage 35 is shifted into an open state,communicates with the first pilot chamber 30, and communicates with thefirst pressure guiding passage 38 through the first pilot chamber 30. Inaddition, the second passage 36 is held in the open state andcommunicates with the annular groove 29 c. With such a configuration,the first hydraulic chamber 16 communicates with the high-pressurechamber 23. Because the second hydraulic chamber 17 communicates withthe suction passage 22 through the drain passage 40, as the pressure inthe first hydraulic chamber 16 is increased, the amount of eccentricityof the cam ring 4 is reduced. In other words, when the pressure in thefirst hydraulic chamber 16 is increased and the force received by thecam ring 4 from the first hydraulic chamber 16 exceeds the sum of theforce received by the cam ring 4 from the cam spring 18 and the forcereceived by the cam ring 4 from the internal pressure of the cam ring 4,the cam ring 4 is moved in the direction in which the amount ofeccentricity with respect to the rotor 2 is reduced.

As described above, when the thrust force exerted by the differentialpressure between the first pilot chamber 30 and the second pilot chamber31 exceeds the biasing force exerted by the return spring 32, the spool29 of the control valve 27 is moved so as to compress the return spring32.

The working oil at the upstream side and the downstream side of theorifice 37 serving as the restrictor, which is interposed in thedischarge passage 24 and imparts resistance to the flow of the workingoil, is respectively guided to the first pilot chamber 30 and the secondpilot chamber 31. In other words, the working oil in the high-pressurechamber 23 is guided directly to the first pilot chamber 30 through thefirst pressure guiding passage 38 without passing through the orifice37, and is also guided to the second pilot chamber 31 through theorifice 37. Therefore, the spool 29 is moved in accordance with thedifferential pressure between upstream and downstream of the orifice 37.

Next, operation of the vane pump 100 will be described with reference toFIGS. 4 to 6. FIGS. 4 to 6 are hydraulic circuit diagrams of the vanepump 100 and respectively show states in which the amount ofeccentricity of the cam ring 4 with respect to the rotor 2 is atmaximum, intermediate, and minimum levels.

As the rotor 2 is rotated by motive force transmitted from the drivingsource to the driving shaft 1, the working oil is sucked from thesuction passage 22 through the suction port 20 into the pump chambers 11whose spaces are expanded between the respective vanes 3 with therotation of the rotor 2. In addition, the working oil is dischargedthrough the discharge port 21 to the high-pressure chamber 23 from thepump chambers 11 whose spaces are contracted between the respectivevanes 3. The working oil that has been discharged to the high-pressurechamber 23 is supplied to the hydraulic apparatus through the dischargepassage 24.

When the working oil passes through the discharge passage 24, thedifferential pressure is generated between upstream and downstream ofthe orifice 37, which is interposed in the discharge passage 24, and thepressures at the upstream and downstream sides of the orifice 37 areguided to the first pilot chamber 30 and the second pilot chamber 31,respectively. The spool 29 of the control valve 27 slides to theposition at which the thrust force exerted by the differential pressurebetween the first pilot chamber 30 and the second pilot chamber 31 isbalanced with the biasing force exerted by the return spring 32.

Because the rotation speed of the rotor 2 is low and a pump dischargeflow amount is small at a pump starting time at which the rotation speedof the rotor 2 is equal to or lower than a predetermined rotation speed,the differential pressure between upstream and downstream of the orifice37 is small, and the thrust force exerted by the differential pressurebetween the first pilot chamber 30 and the second pilot chamber 31 issmall. Therefore, the biasing force exerted by the return spring 32 isgreater than the thrust force exerted by the differential pressurebetween the first pilot chamber 30 and the second pilot chamber 31, andthe return spring 32 is in an elongated state.

In this case, as shown in FIG. 4, because the first passage 35 and thesecond passage 36 open at the annular groove 29 c, the first hydraulicchamber 16 communicates with the drain passage 40 through the annulargroove 29 c and the second hydraulic chamber 17. In this state, becausethe hydraulic pressure that makes the cam ring 4 swing around does notact on the first hydraulic chamber 16 and the second hydraulic chamber17, the cam ring 4 is biased by the cam spring 18 in the direction inwhich the amount of eccentricity with respect to the rotor 2 isincreased. With such a configuration, the amount of eccentricity of thecam ring 4 with respect to the rotor 2 is maximized.

In a region in which the rotation speed of the rotor 2 is equal to orlower than the predetermined rotation speed, the amount of eccentricityof the cam ring 4 with respect to the rotor 2 is maximized to cause thepump displacement volume per rotation of the rotor 2 to be maximized,and the pump discharge flow amount of the vane pump 100 becomes the flowamount substantially in proportion to the rotation speed of the rotor 2.Therefore, even when the rotation speed of the rotor 2 is low, it ispossible to supply the working oil to the hydraulic apparatus at asufficient flow amount.

As the rotation speed of the rotor 2 is increased, the differentialpressure between upstream and downstream of the orifice 37 is increased,and thereby, the thrust force exerted by the differential pressurebetween the first pilot chamber 30 and the second pilot chamber 31 isbalanced with or becomes slightly greater than the biasing force exertedby the return spring 32. With such a configuration, the spool 29 startsto move against the biasing force exerted by the return spring 32.

Furthermore, when the rotation speed of the rotor 2 is increased andreaches the predetermined rotation speed, as shown in FIG. 5, by themovement of the spool 29, the first passage 35 is shifted into the openstate and communicates with the first pilot chamber 30 and the annulargroove 29 c, and the second passage 36 is held in the open state. Withsuch a configuration, because the first hydraulic chamber 16communicates with the high-pressure chamber 23 and the second hydraulicchamber 17 communicates with the drain passage 40, as the pressure inthe first hydraulic chamber 16 is increased, the cam ring 4 starts tomove in the direction in which the amount of eccentricity with respectto the rotor 2 is reduced.

In a region in which the rotation speed of the rotor 2 exceeds thepredetermined rotation speed, the pump discharge flow amount of the vanepump 100 becomes substantially constant. In other words, when the firstpassage 35 and the second passage 36 are shifted into the open state andthe cam ring 4 starts to move in the direction in which the amount ofeccentricity with respect to the rotor 2 is reduced, the pump dischargeflow amount is reduced and the differential pressure between upstreamand downstream of the orifice 37 is reduced. With such a configuration,the return spring 32 is elongated, and the first passage 35 is closedagain. When the first passage 35 is closed, the cam ring 4 is moved inthe direction in which the amount of eccentricity with respect to therotor 2 is increased and the pump discharge flow amount is increased.When the pump discharge flow amount is increased, the differentialpressure between upstream and downstream of the orifice 37 is increased,and the spool 29 is moved so as to compress the return spring 32, andthereby, the first passage 35 and the second passage 36 are againshifted into the open state. As described above, because a control isperformed such that the first passage 35 is opened/closed to make thedifferential pressure between upstream and downstream of the orifice 37constant, the pump discharge flow amount becomes substantially constant.

In a region in which the rotation speed of the rotor 2 exceeds thepredetermined rotation speed, as the rotation speed of the rotor 2 isincreased, because the amount of movement of the spool 29 whilecompressing the return spring 32 is increased and an opening degree ofthe first passage 35 is increased, the amount of eccentricity of the camring 4 with respect to the rotor 2 is reduced gradually, causing agradual reduction in the pump displacement volume per rotation of therotor 2.

When the rotation speed of the rotor 2 is further increased, as shown inFIG. 6, the amount of eccentricity of the cam ring 4 with respect to therotor 2 is minimized, and the pump displacement volume per rotation ofthe rotor 2 is minimized.

Even in a state shown in FIG. 6 in which the amount of eccentricity ofthe cam ring 4 with respect to the rotor 2 is minimized, because theamount of eccentricity does not become zero, the vane pump 100discharges the working oil at the minimum discharge capacity.

As described above, the spool 29 is moved in accordance with the changein the rotation speed of the rotor 2 and the first passage 35 isopened/closed by the movement of the spool 29, and thereby, the pumpdischarge flow amount is adjusted. More specifically, at the pumpstarting time at which the rotation speed of the rotor 2 is equal to orlower than the predetermined rotation speed, because the first passage35 is closed by the spool 29, the amount of eccentricity of the cam ring4 with respect to the rotor 2 is maximized, and the pump discharge flowamount is increased along with the increase in the rotation speed of therotor 2. In addition, when the rotation speed of the rotor 2 exceeds thepredetermined rotation speed, because a control is performed such thatthe opening degree of the first passage 35 is adjusted by the movementof the spool 29 and the differential pressure between upstream anddownstream of the orifice 37 becomes constant, the pump discharge flowamount becomes substantially constant.

Here, when the rotation speed of the rotor 2 is reduced from the regionin which the rotation speed of the rotor 2 is greater than thepredetermined rotation speed, the thrust force exerted by thedifferential pressure between the first pilot chamber 30 and the secondpilot chamber 31 is reduced, and the spool 29 slides in the direction inwhich the return spring 32 is elongated. When the communication betweenthe first passage 35 and the first pilot chamber 30 is shut off by theslide of the spool 29, the high-pressure working oil that has beenguided to the first hydraulic chamber 16 is discharged to the annulargroove 29 c, and then, supplied to the second hydraulic chamber 17through the second passage 36. The working oil in the second hydraulicchamber 17 is subsequently returned to the suction passage 22 throughthe drain passage 40 (see FIGS. 4 and 5).

With such a configuration, when the amount of eccentricity of the camring 4 is increased as the rotation speed of the rotor 2 is reduced, thecam ring 4 receives the force exerted, in the direction in which theamount of eccentricity is increased, by the working oil pressure thathas been guided from the first hydraulic chamber 16 to the secondhydraulic chamber 17 through the annular groove 29 c.

Because the working oil pressure that has been guided to the secondhydraulic chamber 17 is greater than the working oil pressure in thesuction passage 22 that always communicates with the second hydraulicchamber 17 through the drain passage 40, it is possible to make the camring 4 eccentric with higher responsiveness compared to a case in whichthe amount of eccentricity of the cam ring 4 is increased only by thebiasing force exerted by the cam spring 18 and the force exerted by theinternal pressure of the cam ring 4. Thus, it is possible to prevent afollow-up delay of the cam ring 4 when the rotation speed of the rotor 2is reduced.

With the above-mentioned first embodiment, the following effects can beafforded.

When the working oil in the first hydraulic chamber 16 is discharged toincrease the amount of eccentricity of the cam ring 4 as thedifferential pressure between upstream and downstream of the orifice 37is reduced, the working oil that has been discharged from the firsthydraulic chamber 16 to the annular groove 29 c is guided to the secondhydraulic chamber 17 through the second passage 36.

With such a configuration, when the rotation speed of the rotor 2 isreduced and the amount of eccentricity of the cam ring 4 is increased,in addition to the biasing force exerted by the cam spring 18, the forceexerted by the working oil pressure in the second hydraulic chamber 17that has been guided from the first hydraulic chamber 16 through theannular groove 29 c acts on the cam ring 4. Therefore, it is possible toprevent the follow-up delay of the cam ring 4.

Furthermore, because the second passage 36 opens at the valveaccommodating hole 26 and opens at the inner circumferential surface ofthe adapter ring 12 in the second hydraulic chamber 17 by penetratingthrough the adapter ring 12, it is possible to shorten a distancebetween the control valve 27, which is arranged radially outside of theadapter ring 12 so as to be adjacent to the adapter ring 12, and thesecond hydraulic chamber 17.

With such a configuration, when the rotation speed of the rotor 2 isreduced and the amount of eccentricity of the cam ring 4 is increased,it is possible to reduce the time required for the working oil pressure,which has been discharged to the annular groove 29 c from the firsthydraulic chamber 16, to be supplied to the second hydraulic chamber 17.Thus, it is possible to improve a startup of the working oil pressure inthe second hydraulic chamber 17 that biases the cam ring 4 in thedirection in which the amount of eccentricity is increased and preventthe follow-up delay of the cam ring 4 more reliably.

Second Embodiment

A variable displacement vane pump 200 according to a second embodimentof the present invention will be described with reference to FIGS. 7 and8.

The variable displacement vane pump 200 in this embodiment differs fromthat in the first embodiment in a configuration of a second passage 136,and other points are the same as those in the first embodiment.Therefore, components that are the same as those in the first embodimentare assigned the same reference signs, and descriptions thereof shall beomitted.

The second passage 36 is formed so as to open at the valve accommodatinghole 26 and to open at the second hydraulic chamber 17 by penetratingthrough the adapter ring 12 in the first embodiment, whereas in thisembodiment, the second passage 136 serving as a guiding passage isconstituted of the low-pressure chamber 25 and a straight passage 101,which serves as a second guiding passage that connects the back-most endportion of the low-pressure chamber 25 and the annular groove 29 c ofthe control valve 27 in a straight line.

With such a configuration, the working oil that has been discharged fromthe first hydraulic chamber 16 to the annular groove 29 c of the controlvalve 27 is guided to the second hydraulic chamber 17 through thestraight passage 101 and the low-pressure chamber 25.

With the above-mentioned second embodiment, the following effects can beafforded.

Because the second passage 136 opens at the bottom surface 6 b of thepump accommodating recessed portion 6 a in the suction region in whichthe volumes of the pump chambers 11 are expanded, a through hole needsnot be provided in the adapter ring 12, which defines an accommodatingspace on the outer circumferential side of the cam ring 4. Thus, thereis no need to provide the through hole in the adapter ring 12, and inaddition to that, there is no need to perform alignment of the throughhole of the adapter ring 12 and a hole formed in the pump body 6 so asto communicate with the annular groove 29 c of the control valve 27.Therefore, it is possible to prevent the follow-up delay of the cam ring4 while reducing the manufacturing cost.

Furthermore, because the second passage 136 is constituted of thelow-pressure chamber 25 that is formed in a straight line parallel tothe driving shaft 1 and the straight passage 101 that connects theback-most end portion of the low-pressure chamber 25 and the annulargroove 29 c of the control valve 27 in a straight line, it is possibleto form the second passage 136 in the pump body 6 only by providing twostraight passages. Therefore, it is possible to improve the ease ofprocessing for providing the second passage 136 and to reduce themanufacturing cost.

Furthermore, because a part of the second passage 136 is constituted ofthe low-pressure chamber 25, it is possible to form the second passage136 only by providing the straight passage 101. Therefore, it ispossible to further improve the ease of processing for providing thesecond passage 136 and to further reduce the manufacturing cost.

Embodiments of this invention were described above, but the aboveembodiments are merely examples of applications of this invention, andthe technical scope of this invention is not limited to the specificconstitutions of the above embodiments.

For example, in the above-mentioned embodiment, although a case in whichthe working oil is used as the working fluid has been described, otherfluids than the working oil, such as water, aqueous alternative fluid,and so forth, may be used.

Furthermore, in the above-mentioned embodiment, although a case in whichthe low-pressure chamber 25 and the straight passage 101 are both formedin a straight line is described, the configuration is not limitedthereto, and at least one of the low-pressure chamber 25 and thestraight passage 101 may be formed to have a curved shape or a shapehaving a bent portion at an intermediate position.

This application claims priority based on Japanese Patent ApplicationNo. 2014-239200 filed with the Japan Patent Office on Nov. 26, 2014, theentire contents of which are incorporated into this specification.

1. A variable displacement vane pump comprising: a rotor linked to adriving shaft; a plurality of vanes provided so as to be movable in areciprocating manner in the radial direction with respect to the rotor;a cam ring in which tip-end portions of the vanes are in sliding contactwith a cam face on an inner circumference of the cam ring with rotationof the rotor arranged in the cam ring, the cam ring being capable ofbeing made eccentric with respect to the rotor; pump chambers definedbetween the rotor and the cam ring by being partitioned by the pluralityof vanes; a first fluid pressure chamber and a second fluid pressurechamber defined in an accommodating space on an outer circumferentialside of the cam ring; a biasing member configured to always bias the camring in a direction in which an amount of eccentricity is increased; arestrictor configured to impart resistance to flow of working fluiddischarged from the pump chambers; a control valve configured to reducethe amount of eccentricity of the cam ring by introducing the workingfluid that has been discharged from the pump chambers to the first fluidpressure chamber as a differential pressure between upstream anddownstream of the restrictor is increased, the control valve beingconfigured to increase the amount of eccentricity of the cam ring bydischarging the working fluid in the first fluid pressure chamber as thedifferential pressure between upstream and downstream of the restrictoris reduced; a suction passage configured to guide the working fluid tobe sucked into the pump chambers, the suction passage being configuredto always communicate with the second fluid pressure chamber; and aguiding passage configured to allow communication between the controlvalve and the second fluid pressure chamber, the guiding passage beingconfigured to guide the working fluid, which is discharged from thefirst fluid pressure chamber to the control valve, to the second fluidpressure chamber.
 2. The variable displacement vane pump according toclaim 1, further comprising: an adapter ring formed in an annular shapeso as to surround the cam ring; and a pump body that has a recessedportion for accommodating the adapter ring, wherein the control valve isarranged radially outside of the adapter ring so as to be adjacent tothe adapter ring, and the guiding passage opens at an innercircumferential surface of the adapter ring in the second fluid pressurechamber.
 3. The variable displacement vane pump according to claim 1,further comprising a pump body that has a recessed portion foraccommodating the cam ring and that has the guiding passage formedtherein, wherein the guiding passage opens at a bottom surface of therecessed portion in a suction region in which volumes of the pumpchambers are expanded.
 4. The variable displacement vane pump accordingto claim 3, wherein the guiding passage has a first guiding passage anda second guiding passage, the first guiding passage opening at thebottom surface of the recessed portion, the first guiding passage beingformed in a straight line parallel to the driving shaft, the secondguiding passage being configured to connect the first guiding passageand the control valve in a straight line.